On the mechanically driven rapid crystallization of amorphous Si3N4 ceramics

Abstract

The effect of high-energy ball milling on the structure of nanometer sized amorphous ceramics, a-Si3N4 and a-Si–N–C, respectively, has been investigated. At high milling intensity, a-Si3N4 may rapidly crystallize into a mixture of α-Si3N4 and β-Si3N4 after the initial 4 s of milling whereas no structural changes were observed at low milling intensity. For a-Si–N–C, mechanical milling does not cause structural changes at both low and high intensity. It was found that extension of mechanical milling of these hard ceramics can introduce large volume fractions of contamination fragments from the milling media. We conclude that the observed structural changes occurring in a-Si3N4 may be due to mechanical effect, rather than local heating and/or impurity effect.

Nano-Crystalline Structure in Mg₂Si/Mg-2.5Er-5Zn Composite on the Route of Repeated Plastic Working Process

“…However, the diffusion of atoms is rather localized, thus, in order to complete such in-situ synthesis reaction, the driving force for growing of the Mg 2 Si new phase is necessary. Fan et al [11] reported the mechanically driven rapid crystallization of amorphous Si 3 N 4 , and concluded that the crystallization of a-Si 3 N 4 could be attributed to the presence of mechanical force applied by the milling balls and vials during mechanical milling. According to the results of XRD and microstructures, it is suggested that the RPW process can provide a excess driving force for synthesized Mg 2 Si like the ball milling, and it will facilitate the in-situ synthesie reaction completely.…”

Fracture of a Commercial Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 Bulk-Metallic Glass

“…within the shear bands, as previously reported. [5][6][7][8][9][10][11] The localized plastic deformation within the shear bands causes a sudden temperature rise in the BMG alloys, [9,[12][13][14][15][16][17][18][19] which results in a dramatic softening of the material. Such softening of the materials can lead to a catastrophic propagation of a single dominant shear band and the eventual fracture of the BMG alloys.…”